As railroads push to increase car capacity to handle the increasing demands on the transportation network, freight car designers/builders have been stepping up to the challenge. With the overall train lengths limited by system constraints such as passing siding lengths, the challenge has been how to achieve more railcar capacity in the same or shorter lengths of freight cars and trains. Freight car designers/builders have heretofore met this challenge by pushing the top and bottom of the defined clearance line envelopes to the limits allowed by the Association of American Railroads (the “AAR”). Additionally, car designers/builders have utilized modern design tools to make freights car designs lighter in weight, while still meeting the AAR standard design loads whereby allowing each freight car to carry more lading while maintaining maximum allowable gross rail loads.
During the process of assembling or “making-up” a freight train, railcars are run into and collide with each other to couple them together. Since time is money, the speed at which the railcars are coupled has significantly increased. Moreover, and because of their increased capacity, the railcars are heavier than before. These two factors and others have resulted in increased damages to the railcars when they collide and, frequently, to the lading carried within such railcars.
Providing an energy absorption/coupling system at opposed ends of each railcar has long been known. Such a system typically includes a coupler for releasably attaching two railcars to each other and a draft gear assembly arranged in operable combination with each coupler for absorbing, dissipating and returning energy imparted thereto during make-up of the train consist and during operation of the railcar. As railroad car designer/builders have reduced the weight of their designs, however, they have also identified a need to protect the integrity of the railcar due to excessive longitudinal loads being placed thereon, especially as the railcars are coupled to each other. Such longitudinal loads frequently exceed the design loads set by the AAR.
While conventional draft gears have high shock absorbing capacities and capabilities, they tend to transmit a high magnitude of force to the railcar structure during a work cycle. Of course, transmitting a high magnitude of force to the railcar structure can result in damages to the goods being carried by the railcar and the railcar itself.
A conventional draft gear assembly is disposed within a pocket defined by a centersill on the railcar and has an operative length of travel in one direction of movement of about 3.5 inches before solid stops limit the travel and no more energy can be absorbed by the draft gear. Over this limited distance, the energy of the moving railcar must be absorbed so as to reduce the impact forces and resulting damage to the adjacent railcar to be coupled thereto. Largely because of their increased coupling speeds and the increased weights of the loads being carried thereby, heretofore known energy absorption/coupling systems have been shown to be inadequate. As such, railcars are experiencing severe end-impacts that can cause a complete collapse of the end of the car—resulting in large repair costs—coupled with damage to the lading—resulting in significantly higher insurance premiums.
Increasing the travel of the draft gear assembly may advantageously allow more energy to be absorbed. The challenge of increasing the travel of the draft gear assembly is, however, complicated. Passing sidings and loading facilitates often limit the number of railcars that can be joined to each other in one train. Lengthening the draft gear housing also means lengthening the size or length of the pocket wherein the draft gear assembly is accommodated which requires lengthening the centersill resulting in adding length to the railcar. The length of a railroad car, however, is critical.
By itself, adding to the length of the railcar does not appear problematical. When considering, however, that the railcars are not transported individually but rather as part of a much longer train consist, increasing the length of a single railcar is exponentially multiplied when considering the cumulative or overall length of a 100 railcar train consist. Increasing the length of an individual railcar can result in the last railcar in a 100 car consist no longer fitting on the siding and, thus, having to be left behind. As such, there would be at least a one percent (1%) loss in train efficiency. This is simply unacceptable. Accordingly, the concept of simply increasing the length of the draft gear assembly to solve the problem of energy absorption between railcars is unacceptable to the railroad industry.
Thus, there is a continuing need and desire for a draft gear assembly which not only allows for increased travel over which the high level of energy from impact loads of colliding railcars can be absorbed, dissipated and returned but the overall length of the draft gear assembly housing cannot be lengthened and the draft gear assembly must be capable of absorbing the increased impact loads being realized in today's railroad industry.